HYDROGEN BONDING .63. IR STUDY OF HYDRATION OF DIMETHONIUM AND PENTAMETHONIUM HALIDES AND NMR STUDY OF CONFORMATION OF PENTAMETHONIUM ION IN SOLUTION

摘要

We have investigated hydrate formation by dimethonium and pentamethonium - (CH3N+-(CH2)(n)-N-+(CH3)(3) where n = 2 and 5 - bromide, chloride, and fluoride. Dimethonium bromide forms a dihydrate which contains a C-2h(H2O . Br-)(2) planar cluster. Dimethonium chloride forms a hypobarogenic dihydrate which is crystalline at reduced pressure but disproportionates to anhydrous material and liquid hexahydrate. Dimethonium fluoride forms three hydrates, a hexahydrate, tetrahydrate, and dihydrate. These hydrates, which represent fluoride ion trihydrate, dihydrate, and monohydrate respectively, have water-fluoride structures similar to those observed for a variety of other quaternary ammonium fluoride hydrates of corresponding stoichiometry; the dihydrate contains C-2h(H2O . F-)(2) clusters. Pentamethonium bromide and chloride form crystalline dihydrates (halide ion monohydrates) which do not contain planar (H2O . X(-))(2) clusters. Pentamethonium fluoride forms a trihydrate with unknown structure and, unlike other quaternary ammonium fluorides, does not form a fluoride ion monohydrate with (H2O . F-)(2) clusters. The fact that the odd-numbered pentamethonium ion (C-2v) fails to form halide dihydrates with planar (H2O . X(-))(2) clusters while the even-numbered dimethonium, hexamethonium, and decamethonium ions (C-2h) all do may be a function of ion symmetry; however, further studies are required to clarify this point. FT-NMR study of the pentamethonium ion in aqueous solution and molecular modeling shows that rotation about the C1-C2 and C4-C5 sigma-bonds is not possible, while rotation about the C2-C3 or C3-C4 bonds does take place. [References: 24]